Ethane Conversion Xiomaries Torres and Dr. Juan Lopez

8/9/2019 Ethane Conversion Xiomaries Torres and Dr. Juan Lopez

1/13

University of Puerto Rico at CayeyLaboratory of Modeling, Simulations and Theory

Building Research Infrastructure and Capacity

Comparative Energetics of Reaction Steps Involved inAlkane Metathesis on a Silica vs Porous Organic

Polymer Supported Ta-Alkyl Catalyst:

A Computational Study

Xiomaries Torres GarcíaChemistry Department, UPR-Cayey

Dr. Juan M. López EncarnaciónMath-Physics Department, UPR-Cayey

Dr. Julius JellinekChemical Sciences and Engineering Division

Argonne National Laboratory


2/13

Global concept of projectSupport Synthesis Metal Incorporation

CH 4 +2C 2H 6

Application


3/13

• 2005: Prof. R. Schrock “ Massachussets Institute of Technology USA ” y Dr.Y. Chauvin “ Institut Francais du Pètrole France ” – Nobel Prize:contribution “Development of metathesis method in organic synthesis” .

• Grubbs and his co-workers developed versatile catalysts using Ruthenium

metal.

Dr. Y. Chauvin Prof. R. Schrock Robert H. Grubb

One of Schrock’s molybdenum catalysts

García, G.; Herrera, K.; Gril lasca, I; Acosta, A. Desarrollo del método de metátesis en síntesis orgánica . Premio Nobel de Química. 2006 , 39-44.

Metathesis Reactions


4/13

Metathesis of alkanes and alkenes• Discovered: 1950• Different types of metathesis• Breaking and bond formation of hydrocarbons in a process catalyzed by

certain metal complexes• Convert a hydrocarbon: one carbon atom more or less• The transformation of alkanes to homologs of different chain lengths

Recovered:http://www.yteach.co.za/index.php/resources/alkenes_isomeris_double_bond_reaction_bromine_addition_reaction_hydrogenation_t_page_6.html The Nobel Prize in Chemistry 2005 • The Royal Swedish Academy of Sciences

Recovered: http://imgkid.com/alkanes-alkenes-alkynes.shtml


5/13

The problem

2C nH2(n)+2 Cn-iH2(n-i)+2 + C n+iH2(n+i)+2

The main problem in any metathesis reactions is theenergy required to form and break the C-H and C-C

bonds. Our test reaction is the conversion of ethane into propane and methane promoted by a POP-Ta-Alkylcatalyst.

Basset, J.; Copéret, C .; Soulivong, D.; Taoufik, M.; Cazat, J. Accounts of Chemical Research. 2010 , 43, 323-334.

POP-Ta-Alkyl


6/13

• General:•

Decrease the activation energies of the ethane metathesis ascompare with silica support by using a novel catalyst whichhas a porous organic polymer as support

• Specifics:• Propose a reaction mechanism for ethane conversion

through a POP-Ta-Alkyl• Propose different organic ligands to mimic the amorphous

POPs and incorporate the Ta-Alkyl complex on it•

Design and compute the Gibbs free energies at differenttemperatures for molecular models of reactants,intermediates, transition states, and products involve in thereaction mechanism for each organic ligand

• Build graphs of the reaction energy profile

Objectives


7/13

Justification• Metathesis of alkane and alkenes have large number of

applications, for example:• Obtaining wide variety of molecules• High yields of important pharmaceutical compounds• Reformulation of fuel• Industrial Chemistry• Energetic Aspect

• Advantages of porous organic polymers as support of single-metal reaction centers

• Thermal stability• Robust and yet flexible (allowing possible twisting which

help in reducing the energy barriers)

López, J.; Tanabe, K.; Johnson, M.; Jellinek, J. Chem. Eur. J. 2013 , 19, 13646-13651.


8/13

2C2H6 CH4 + C3H8gProposed Mechanism

Proposed Mechanism for Ethane Metathesis

8

1

3

4

2

7

6 5

[Ta] Catalyst

The numbers label reaction steps

I

II

III

IV

POP-P5-O 2-T5

POP-P2-O 2-T5

POP-P2-(NCH 3)2-T5

Silica-T5

g

Molecular Models of Ta-Alkyl (T5)Catalyst on Different Supports


9/13

Molecular ligands proposed as model of the porous organic polymers

POP-1

POP-1-Extended


10/13

Computational MethodologyQuantum Mechanics

Density Functional TheoryPW91-Exchange and

Correlation FunctionalDesign of molecular models

Transfer data fromsupercomputer Analysis of the results


11/13

[ Ta ] Catalyst

The computations identify catalyst IV as a superior synthetic target. Its primarydifference from the other three catalysts is that it furnishes an N-typecoordination environment to the Ta reaction center instead of an O-type (see themolecular models in the preceding slide).

I

II

III

IV

g

2C2H

6 CH

4 + C

3H

8g

[Ta] Catalyst

Support Effects in Ethane Metathesis:Comparative Energetics

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.21.4

1 2 3 4 5 6 7 8

E x o

t h e r m

i c i t y

Δ E ( e V )

Reaction step


12/13Basset, J.; Schinzel, S.; Chermette, H.; Copéret, C . J. Am. Chem. Soc. 2008 , 130, 7984-7987.

Test example: Carbene Hydride Mechanism

EnergyProfile

Molecularcomplexes

involved in thetop reactionmechanism


13/13

Ethane Conversion Xiomaries Torres and Dr. Juan Lopez

Documents

Transcript of Ethane Conversion Xiomaries Torres and Dr. Juan Lopez